3. Steps of Fertilization
• Several sperm penetrate corona radiata.
• Several sperm attempt to penetrate zona pellucida.
• One sperm enters egg and nuclei fuse, producing a zygote.
• Egg’s plasma membrane and zona pellucida change to prevent
polyspermy.
4.
5.
6. Entry of Ovum into Fallopian Tube
• 3 to 5 days is normally required
• Transport is effected mainly by:
1. A feeble fluid current in the tube resulting from epithelial
secretion
2. Action of the ciliated epithelium that lines the tube; the cilia
always beat toward the uterus activated by estrogen from the
ovaries
3. Weak contractions of the fallopian tube may also aid passage of
the ovum
7.
8. Implantation of Blastocyst in Uterus
• Before implantation, the blastocyst obtains its nutrition from the
uterine endometrial secretions, called “uterine milk”
• Implantation results from the action of trophoblast cells that develop
over the surface of the blastocyst
• Trophoblast cells secrete proteolytic enzymes that digest and liquefy
the adjacent cells of the uterine endometrium
• Once implantation has taken place, the trophoblast cells and decidual
cells proliferate rapidly, forming the placenta
9.
10.
11. Placenta
• Site of metabolic and nutritional exchange
• Maternal side – decidua basalis
• Fetal side – amnion
• 15 – 20 cotyledons: contain the complex vascular system of villi
12.
13.
14. Functions of Placenta
1. Transfer gasses
2. Transport nutrients
3. Excretion of wastes
4. Hormone production – temporary endocrine organ hCG, hPL,
estrogen and progesterone
5. Formation of a barrier – incomplete, nonselective – alcohol, steroids,
narcotics, anesthetics, some antibiotics and some organisms can
cross
15. Placental Transport
• Simple diffusion water, oxygen, carbon dioxide, sodium and
chloride
• Facilitated transport glucose and galactose
• Active transport amino acids, calcium, iron, iodine and vitamins